launchArguments in UITesting in Xcode 7.3 not working

I've been writing UI tests in Xcode 7.3 and recently wanted to add a launch argument to enable some test code inside the app. I initially tried setting

XCUIApplication().launchArguments

as several people have done in various posts, but they would not work.

Digging around it appears that both

launchArguments

and

launchEnvironment

cannot be setup within a UI test, even though the API documentation says they can.

Further when I attempted to set launch arguments and environment variables in the UI Testing scheme, they also where not passed through to the app, where as when unit testing or running the app, they are.

Here's a copy of a quick tests I did to prove this, all these tests fail.